Implantable microstimulators, also known as BION devices (where BION is a registered trademark of Advanced Bionics Corporation, of Sylmar, Calif.), are typically characterized by a small, cylindrical housing which contains electronic circuitry that produces electric currents between spaced electrodes. These microstimulators are implanted proximate to target tissue, and the currents produced by the electrodes stimulate the tissue to reduce symptoms or otherwise provide therapy for various disorders. An implantable battery-powered medical device may be used to provide therapy for various purposes including nerve or muscle stimulation. For example, urinary urge incontinence may be treated by stimulating the nerve fibers proximal to the pudendal nerves of the pelvic floor; erectile or other sexual dysfunctions may be treated by providing stimulation of the cavernous nerve(s); and other disorders, e.g., neurological disorders caused by injury or stroke, may be treated by providing stimulation of other appropriate nerve(s).
Implantable microstimulators have been disclosed that provide therapy for neurological disorders by stimulating the surrounding nerves or muscles. Such devices are characterized by a sealed housing which contains electronic circuitry for producing electric currents between spaced electrodes. A microstimulator is precisely implanted proximate to the target tissue area and the electrical currents produced at the electrodes stimulate the tissue to reduce the symptoms and otherwise provide therapy for the neurological disorder.
A battery-powered microstimulator of the present invention is preferably of the type referred to as a BION device, which may operate independently, or in a coordinated manner with other implanted devices, or with external devices.
By way of example, in U.S. Pat. No. 5,312,439, entitled Implantable Device Having an Electrolytic Storage Electrode, an implantable device for tissue stimulation is described. U.S. Pat. No. 5,312,439 is incorporated herein by reference. The described microstimulator shown in the '439 patent relates to an implantable device using one or more exposed, electrolytic electrodes to store electrical energy received by the implanted device, for the purpose of providing electrical energy to at least a portion of the internal electrical circuitry of the implantable device. It uses an electrolytic capacitor electrode to store electrical energy in the electrode when exposed to body fluids.
Another microstimulator known in the art is described in U.S. Pat. No. 5,193,539, “Implantable Microstimulator,” which patent is also incorporated herein by reference. The '539 patent describes a microstimulator in which power and information for operating the microstimulator is received through a modulated, alternating magnetic field in which a coil is adapted to function as the secondary winding of a transformer. The induction coil receives energy from outside the body and a capacitor is used to store electrical energy which is released to the microstimulator's exposed electrodes under the control of electronic control circuitry.
In U.S. Pat. Nos. 5,193,540 and 5,405,367, which patents are incorporated herein by reference, a structure and method of manufacture of an implantable microstimulator is disclosed. The microstimulator has a structure which is manufactured to be substantially encapsulated within a hermetically-sealed housing inert to body fluids, and of a size and shape capable of implantation in a living body, with appropriate surgical tools. Within the microstimulator, an induction coil receives energy from outside the body requiring an external power supply.
In yet another example, U.S. Pat. No. 6,185,452, which patent is likewise incorporated herein by reference, there is disclosed a device configured for implantation beneath a patient's skin for the purpose of nerve or muscle stimulation and/or parameter monitoring and/or data communication. Such a device contains a power source for powering the internal electronic circuitry. Such power supply is a battery that may be externally charged each day. Similar battery specifications are found in U.S. Pat. No. 6,315,721, which patent is additionally incorporated herein by reference.
Other microstimulator systems prevent and/or treat various disorders associated with prolonged inactivity, confinement or immobilization of one or more muscles. Such microstimulators are taught, e.g., in U.S. Pat. No. 6,061,596 (Method for Conditioning Pelvis Musculature Using an Implanted Microstimulator); U.S. Pat. No. 6,051,017 (Implantable Microstimulator and Systems Employing the Same); U.S. Pat. No. 6,175,764 (Implantable Microstimulator System for Producing Repeatable Patterns of Electrical Stimulation; U.S. Pat. No. 6,181,965 (Implantable Microstimulator System for Prevention of Disorders); U.S. Pat. No. 6,185,455 (Methods of Reducing the Incidence of Medical Complications Using Implantable Microstimulators); and U.S. Pat. No. 6,214,032 (System for Implanting a Microstimulator). The applications described in these additional patents, including the power charging techniques, may also be used with the present invention. The '596, '017, '764, '965, '455, and '032 patents are incorporated herein by reference.
It is also known in the art to use thermal energy to power an at least partially implantable device, as taught in U.S. Pat. No. 6,131,581, also incorporated herein by reference, wherein an implantable thermoelectric energy converter is disclosed.
Despite the various types of microstimulators known in the art, as illustrated by the examples cited above, significant improvements are still possible and desirable, particularly relative to a microstimulator having a bi-directional telemetry system that allows communications with the microstimulator once implanted, coupled with a self-contained primary or rechargeable battery that:    (a) accommodates the various needs of a microstimulator; (b) accommodates various locations in the implanted site; (c) allows the microstimulator to operate longer between charges or replacement, and/or (d) allows better and easier control and/or monitoring of the implanted microstimulator.